Dear Mamta, the short sequences of DNA Nucleotides measuring upto 150 to 200 base pairs long in eukaryotes are called Okazaki fragments. These fragments are  first synthesized discontinously and later linked together by an enzyme called DNA Ligase to create the lagging strand of DNA replication. Now if you can picturise the DNA, it is a double helix structure. During DNA replication, this double helix is unwound and the strands are separated by an enzyme called DNA Helicase. Now this process is called DNA replication fork. After the formation of this fork, DNA Primase and DNA Polymerase act together to create a new complementary strand. Now these enzymes can only work when in the 5' to 3' direction. This might result in both the complementary strands wounding in different directions. Now to prevent that, the leading strand undergoes a continuous replication process as its strand has 3' to 5' directional feature. This allows the polymerase assembling resulting the lead strand to follow the replication fork without interruption. the trailing strand now cannot continuosly be created as it still has the 5' to 3' direction which means the polymerase has to work backwards to the front. This causes periodic breaks in the process of creating the trailing strand. So the primase and polymerase move in  opposite direction of the work so the enzymes must stop and start again when DNA Helicase breaks the strands. The newly syntesized fragments are called Okazaki fragments. These are bound by DNA Ligase. Defects in maturation of Okazaki fragments can potentially cause strands in the DNA to break and cause different forms of abnormality. This can also change the DNA and causes defects in the genepool of that species in question.